1. Field of the Invention
The present invention relates to an optical head which is capable of both forming a laser spot at the magnetic layer of a magneto-optical disk and supplying an external magnetic field to the magnetic layer of the magneto-optical disk. The present invention also relates to a coil assembly used for such an optical head.
2. Description of the Related Art
Conventionally, various kinds of magneto-optical disk apparatus have been used for writing and reading data in and from a magneto-optical disk. Taking a data-reading method by MSR (magnetically induced super resolution) for example, use may be made of a magneto-optical disk which includes laminated magnetic layers whose magnetic characteristics may vary depending upon temperature. Data stored in such a disk is read out from a region, within a laser spot, which is heated up to a particular temperature by a laser beam. For reading out data from the disk, a magnetic field needs to be supplied to an area corresponding to the laser spot.
To write desired data in the magneto-optical disk, the recording layer of the disk will be irradiated by a laser beam, while being supplied with an external magnetic field. When a region of the recording layer is heated up to or above the Curie temperature by the laser beam, the direction of magnetization in the region may be reversed, meaning that data is stored. For reversing the direction of magnetization, use may be made of e.g. a light modulation method or a magnetic field modulation method. In either way, it is necessary to provide appropriate means for generating an external magnetic field for performing data-recording.
As understood from the above, an apparatus used for writing data in a magneto-optical disk and reading out data therefrom needs to be provided with at least two functions; a first function for forming a laser spot on the surface of the disk, and a second function for generating an external magnetic field to perform the recording or reading of data. For the first function, an optical head is used, while for the second function, a magnetic head is used.
An optical head and a magnetic head may be located separately. Specifically, the former may be arranged in facing relation to the recording surface of the disk (i.e., on the side of the transparent substrate), whereas the latter may be arranged in facing relation to the opposite (back) surface of the disk.
Alternatively, an optical head and a magnetic head may be integrated into a single unit. An example of such a unit is disclosed in JP-A-2(1990)-18720. Referring to FIGS. 17-20 of the present application, the conventional unit (optical head) disclosed in this Japanese document will now be described below.
As shown in FIG. 17, the conventional apparatus includes a spindle (Sp) for rotating a magneto-optical disk (D) attached thereto, an arm (A) movable in radial directions of the disk (D), a mirror (M) mounted on an end of the arm (A), and a slider (S) supported by the arm (A) via a suspension arm (Sa). The slider (S) is provided with an objective lens (L), as shown in FIG. 18, and a coil block (Cb) disposed immediately under the objective lens (L).
As shown in FIG. 18, the coil block (Cb) includes a supporting base (B) and a coil (C) formed on the bottom surface of the supporting base (B). The supporting base (B), which may be made of silicon, is formed with a through hole (a) which resembles a reversed truncated pyramid. The through hole (a) is provided for allowing the passage of a laser beam converged by the objective lens (L). After passing through the hole (a), the converged laser beam reaches the disk (D) and forms a bright spot (Ls) on the disk.
The coil (C) arranged on the bottom surface of the supporting base (B) may be formed by printing a selected pattern of a conductive material on the bottom surface of the supporting base (B). As shown in FIG. 20, the coil (C) surrounds the aperture of the through hole (a) that is open in the bottom surface of the supporting base (B). The through hole (a) is arranged to positionally correspond to the nominal optical axis of the objective lens (L).
As shown in FIG. 17, the arm (A) is caused to move radially of the disk (D) by a linear actuator (Ac) such as a voice coil motor. When the apparatus is not operated, the slider (S) is elastically urged to the disk surface by the suspension arm (Sa) to be held in pressed contact with the disk (D). On the other hand, when the disk (D) is caused to rotate at high speed, the slider (S) will float slightly above the disk (D) by a fluid wedge formed between the slider (S) and the disk (D).
As shown in FIG. 17, the conventional apparatus further includes a stationary module (SM) incorporating a laser emitting unit, a detector, a collimator and so on. In operation, a laser beam is emitted from the module (SM) to travel along the arm (A). Then, the laser beam is reflected by the mirror (M) to go along a path perpendicular to the previous path. Consequently, the laser beam enters the objective lens (L) and is converged by the lens. Consequently, a predetermined laser spot (Ls) is formed on the disk (D).
In the conventional apparatus described above, the coil (C) is disposed so adjacent to the disk (D) as to surround the laser spot (Ls). Thus, a magnetic field needed for performing data-recording or data-reading will be properly applied to a region corresponding to the laser spot (Ls) on the disk (D). However, the conventional apparatus has been found disadvantageous in the following point.
As shown in FIG. 18, the coil (C) of the conventional optical head is not provided with a core. With such an arrangement, the magnetic field to be generated by the coil (C) is rendered weaker than the magnetic field to be generated by a coil provided with a core having a high magnetic permeability.
One way to strengthen the magnetic field to be generated by a coil is to increase the number of turns of the coil. However, as the number of the turns of the coil is increased, the resistance of the coil may unfavorably become greater. In such a case, a higher voltage should be supplied to the coil for causing the coil assembly to work properly. Further, a coil with an increased number of turns may fail to provide an expected response as the voltage frequency supplied to the coil becomes higher. Clearly, it is disadvantageous to use such a coil as an external magnetic field generating means for performing recording of data by magnetic field modulation.
The present invention has been proposed under the above circumstances. The first objective of the present invention is to provide a coil assembly which is capable of providing a required external magnetic field to a magneto-optical disk, wherein the number of turns of the coil is substantially increased without causing the resistance of the coil to become greater. The second objective of the present invention is to provide an optical head which includes both an objective lens for forming a laser spot on a magneto-optical recording medium and a coil for applying an external magnetic field to the magneto-optical recording medium, wherein a suitably arranged core having a high magnetic permeability is used for improving the magnetic field generated by the coil.
According to a first aspect of the present invention, there is provided a coil assembly comprising:
a coil arranged around a predetermined axis; and
a supporting member for carrying the coil, the supporting member being formed with a through hole corresponding to the predetermined axis;
wherein the coil includes a plurality of coil elements connected in parallel.
Preferably, each coil element may have a circular configuration about the predetermined axis.
When each coil element has a circular configuration about a predetermined axis, the following advantage is obtainable. It is now supposed that the number of turns of a coil is equal to xe2x80x9cnxe2x80x9d and the resistance of each coil element is equal to xe2x80x9crxe2x80x9d. In these conditions, the overall resistance Ra of a conventional coil (in which the coil elements are connected in series to provide a single wire) is equal to xe2x80x9crxc3x97n.xe2x80x9d
According to the present invention, on the other hand, the overall resistance Rb of a coil is equal to xe2x80x9cr/nxe2x80x9d, which is smaller than in the above case. Thus, the voltage to be applied to the coil can be made comparatively lower. Further, since the inductance of the coil is also made lower, it is possible to obtain excellent frequency characteristics when the coil assembly is used as an external magnetic field generating means for performing data-recording by a magnetic field modulation method. This means that magnetic field modulation can be properly performed even in a higher range of frequency. Accordingly, the data-recording density for a magneto-optical disk can be further increased.
According to a preferred embodiment, at least part of the coil elements may be concentrically arranged in a common plane. With such an arrangement, the coil assembly can be reduced in thickness.
According to another preferred embodiment, at least part of the coil elements may be spaced from each other along the predetermined axis. With such an arrangement, the outer diameter of the coil can be reduced, which is advantageous in increasing the strength of the magnetic field to be generated.
According to another preferred embodiment, each coil element may have a whirling or spiral configuration, and the through hole of the supporting member may have a circular or polygonal cross section. Corresponding to the through hole, the coil supporting member may have a circular or polygonal configuration. In this embodiment, each coil element is similar to the conventional coil. However, since the coil elements of the present invention are connected in parallel, the same advantages as described above in connection with the previous embodiments are obtained. (It should be noted that the overall resistance Rc of the coil is equal to xe2x80x9cr1/n1xe2x80x9d, when each coil element has the same resistance of r1 and the total number of the coil elements is xe2x80x9cn1.xe2x80x9d)
Preferably, the whirling (or spiral) coil elements may be spaced from each other in the lengthwise direction of the predetermined axis. With such an arrangement, the number of turns of each coil element is advantageously increased. Accordingly, the strength of the magnetic field to be generated is increased.
According to a second aspect of the present invention, there is provided an optical head which incorporates a coil assembly (used as an external magnetic field generating means) according to the first aspect of the present invention. The optical head comprises:
a carriage movable along a surface of a magneto-optical disk;
a suspension member attached to the carriage; and
a slider attached to the suspension member to be brought into facing relation to the surface of the magneto-optical disk, the slider being provided with an objective lens and a coil assembly which includes a coil arranged around a predetermined axis and a supporting member for carrying the coil, the supporting member being formed with a through hole corresponding to the predetermined axis;
wherein the coil includes a plurality of coil elements connected in parallel, the through hole being arranged to correspond to an optical axis of the objective lens.
According to a preferred embodiment, the carriage may comprise an elongated arm movable in a radial direction of the magneto-optical disk. The elongated arm may be provided, at an end thereof, with a mirror for directing a laser beam toward the objective lens.
According to a third aspect of the present invention, there is provided an optical head comprising:
a carriage movable along a surface of a magneto-optical disk;
a suspension member attached to the carriage; and
a slider attached to the suspension member to be brought into facing relation to the surface of the magneto-optical disk, the slider being provided with an objective lens and a coil assembly which is formed with a through hole corresponding to an optical axis of the objective lens;
wherein the optical head further comprises a magnetic member at least part of which is arranged in the through hole of the coil assembly.
With such an arrangement, the portion of the magnetic member arranged in the thorough hole may function as a core having a high magnetic permeability. Thus, as opposed to a coil assembly with no core, the coil assembly having the above arrangement can generate an external magnetic field of a greater power.
Preferably, the magnetic member may be transparent. With such an arrangement, the magnetic member does not prevent the laser beam from passing through the through hole. Thus, it is possible to fill the through hole with a core (the magnetic member) having a sufficiently high magnetic permeability.
Preferably, the objective lens may be made of a transparent magnetic material, and the magnetic member may be integrally formed with the objective lens. With such an arrangement, there is no need to separately prepare a magnetic member as a core for the coil, which is advantageous in reducing the number of necessary components.
According to a preferred embodiment, the magnetic member may comprise a magnetic layer located between the objective lens and the coil assembly.
Preferably, the magnetic member may be provided with a cylindrical portion arranged in the through hole of the coil assembly, and the cylindrical portion may be arranged to taper toward the magneto-optical disk.
Preferably, the objective lens may be provided with a tapering portion arranged in the through hole of the coil assembly. The tapering portion of the magnetic layer may be reflective and arranged to cover the tapering portion of the objective lens. With such an arrangement, the laser beam passing through the objective lens can effectively lead to the magneto-optical disk.
The magnetic member may be formed with a bent portion extending around a circumference of the coil assembly.
The objective lens as a whole may taper toward the magneto-optical disk, the objective lens having a diametrically smaller end arranged in the hole of the coil assembly.
The magnetic member may comprise a magnetic layer formed on a side surface of the objective lens. The magnetic layer may be produced by subjecting a magnetic metal to sputtering for example. In this manner, the magnetic layer can easily be formed on the side surface of the objective lens before the lens is fixed to the coil assembly. Thus, the assembling of the optical head is facilitated.
Advantageously, the magnetic layer may be rendered reflective. To produce such a reflective magnetic layer, use may be made of a reflective metal. With the use of a reflective magnetic layer, it is possible to prevent the laser beam from unduly leaking out via the side surface of the objective lens. Thus, a desired laser spot is properly formed on the magneto-optical disk.
Other objects, features and advantages of the present invention will become clearer from the following detailed description given with reference to the accompanying drawings.